I'm currently in the process of searching for a cheap standalone ecu, but the main limitation of them is the fact that they have only 4 injector outputs. I have heard and read in the ecus documentation that you can pair two injectors together and therefore use three injector outputs for a six cylinder engine and four for a eight cylinder engine. The thing that boggles me is that a solution like this would be inefficient(?). From my understanding let's say in a V6 you pair two injectors wich pistons are at TDC, but they are at different cycles. Only one of them is firing(?). Could I use this for a daily? And what about the ignition?

3 Answers
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Yes, paired injectors is one solution, but have you looked for standalone ecu's with more outputs? It does affect the fuel use obviously, as only one cylinder is firing while the other is closing exhaust and opening inlet.

As for ignition, the same concept applies - double ended coils will work as a spark into a cylinder changing from exhaust to inlet is not an issue.

Ah yes, I see that the paired ignition coils would not be a problem. As for the excess fuel in one cylinder, will the milleage go down by half? Since it would dump fuel at the wrong cycle. Now regarding buying an ECU with more outputs, it's just out of my price range.
– user103320Jun 4 at 13:42

Well I'm an idiot, after doing some more research I came to the conclusion that the mileage would be slightly worse than a sequential injection system. Basically the fuel would sit on top of the valve head in the intake port until the cam opens it.
– user103320Jun 4 at 15:37

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Wasted spark is one thing, wasted injection quite another. I don't like either. (Wasted spark tends to migrate metal and deposit it on the center electrode on the plugs that fire in reverse.) But the paired injection does work, and has been used in the past. Unless you have GDI, the fuel sits in the plenum runners and valve heads to some extent anyway. But certainly atomization and efficiency are affected. I'd save for a true custom "Haltek" setup with the proper number of outputs. Trying to tune paired injectors is also going to be a pain!
– SteveRacerJun 4 at 22:45

@SteveRacer the wasted spark method was used on the 2CV as a really cheap and effective option to remove the need for a troublesome distributor - quite a sensible solution... However, I agree about the waste of fuel...
– Solar MikeJun 4 at 22:51

@SolarMike You are absolutely correct. I used to use a 2CV flat-twin boxer animation to teach wasted spark in vocational college. It also had a speed based ignition advance, with no account for engine load. Paralever suspension, a roll-back fabric roof, and a cheap price. It was the Volkswagen "peoples car" of France (and many other export countries) - and remains one of the most produced vehicles in history.
– SteveRacerJun 4 at 23:07

As an alternative, depending on how cheap a cheap ECU is, you could use the Ferrari method. On the Ferrari V8, they run two ECU's fed from the same crank position sensor. One runs one bank and the other, the other. Of course for this to be cost effective, the difference in price between a 4-cyl ECU and an 8-cyl ECU would have to be significant.

You should define what you mean by "cheap" because what you think is pricey might be cheap to someone else. Even an ECU meant primarily for 4-bangers can be hacked to work with a V6 using wasted spark and 2 squirts per cycle, e.g. Speeduino, one of the cheapest standalone ECUs I know of.